The present invention relates generally to surgical procedures for spinal stabilization and more specifically to instrumentation and techniques for inserting a spinal implant within the intervertebral disc space between adjacent vertebra. More particularly, while aspects of the present invention may have other applications, the invention provides instruments and techniques especially suited for interbody fusion from a generally posterior approach to the spine
Various surgical methods have been devised for the implantation of fusion devices into the disc space. Both anterior and posterior surgical approaches have been used for interbody fusions. In 1956, Ralph Cloward developed a method and instrumentation for anterior spinal interbody fusion of the cervical spine. Cloward surgically removed the disc material and placed a tubular drill guide with a large foot plate and prongs over an alignment rod and then embedded the prongs into adjacent vertebrae. The drill guide served to maintain the alignment of the vertebrae and facilitated the reaming out of bone material adjacent the disc space. The reaming process created a bore to accommodate a bone dowel implant. The drill guide was thereafter removed following the reaming process to allow for the passage of the bone dowel which had an outer diameter significantly larger than the reamed bore and the inner diameter of the drill guide. The removal of the drill guide left the dowel insertion phase completely unprotected. Thus, Cloward's method and instrumentation was designed for and limited to an anterior surgical approach and was inappropriate for a posterior application.
Furthermore, B. R. Wilterberger described in a paper entitled “Dowel Intervertebral Fusion as Used in Lumbar Disc Surgery” (published in The Journal of Bone and Joint Surgery, volume 39A, pgs. 234-92, 1957), the unprotected drilling of a hole from a posterior approach into the lumbar spine between the nerve roots and across the disc space, and then inserting a bone dowel into that disc space. While Wilterberger had taken the Cloward concept of circular drilling followed by dowel fusion and applied it to the lumbar spine from a posterior approach, he had not further improved the method, nor had he advanced the instrumentation to provide adequate protection for the sensitive vessels and neurological structures adjacent to the operating field.
U.S. Pat. No. 5,484,437 to Michelson discloses a technique and associated instrumentation for inserting a fusion device from a posterior surgical approach that provides greater protection for the surrounding tissues and neurological structures during the procedure. As described in more detail in the '437 patent, the surgical technique involves the use of a distractor having a penetrating portion that urges the vertebral bodies apart to facilitate the introduction of the necessary surgical instrumentation. The '437 patent also discloses a hollow sleeve having teeth at one end that are driven into the vertebrae adjacent the disc space created by the distractor. These teeth engage the vertebra to maintain the disc space height during subsequent steps of the procedure following removal of the distractor. In accordance with one aspect of the '437 patent, a drill is passed through the hollow sleeve to remove portions of the disc material and vertebral bone to produce a prepared bore for insertion of the fusion device. The drill is then removed from the sleeve and the fusion device is positioned within the disc space using an insertion tool.
While the more recent techniques and instrumentation represent an advance over earlier surgical procedures for the preparation of the disc space and insertion of the fusion device, the need for improvement still remains. The present invention is directed to this need and provides convenient methods and instruments to insure safe and effective preparation of a disc space in conjunction with implant placement.